Recently, with the growth of mobile communication technologies, portable electronic devices providing various services beyond mere voice calling have become necessities of the modern world. These electronic devices are widely used because of their broad range of functionality. However, deaf persons have many difficulties in using portable electronic devices.
Typically, deaf users operate the electronic devices with the assistance of a hearing aid. A basic structure of the hearing aid is composed of a microphone, an amplifier, and a receiver. The microphone converts an analog signal into a digital signal and sends the digital signal to the amplifier. The amplifier converts an amplified sound into an analog signal and forwards the analog signal to the receiver to provide a voice signal to people with impaired hearing. Also, a telecoil may be installed in the hearing aid to sense an electromagnetic wave generated in the electronic device and provide the electromagnetic wave as a voice signal.
Unfortunately, when deaf users utilize hearing aids in tandem with portable electronic devices, a howling phenomenon takes place. Here, the howling phenomenon refers to an unusual sound generated by a kind of resonance, in which a volume of any specific frequency zone (i.e., an amplitude) increases in geometrical progression because a sound input to the microphone of the hearing aid is repetitively amplified through the amplifier, outputted through the receiver, fed back through the microphone, again amplifying the sound, and again outputting the amplified sound through the receiver, etc.
The United States of America requires by law that electronic device manufacturers implement HAC so that deaf persons suffers no undue inconvenience operation portable electronic devices of the USA. Consumer electronic device manufacturers thus produce electronic device products that are operable by persons with impaired hearing.